Polyvinyl alcohol film and polarizing film

ABSTRACT

The invention is a film of a vinyl alcohol polymer that contains from 0.01 to 20 mol % of cationic group-containing units and contains from 0.5 to 24 mol % of α-olefin units having at most 4 carbon atoms. The polyvinyl alcohol film gives polarizing films and polarizer which are resistant to water and have good polarizing properties and which are free from a problem of irregular coloration.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polyvinyl alcohol film, and toa polarizing film and a polarizer that comprise the polyvinyl alcoholfilm.

[0003] 2. Description of the Prior Art

[0004] A polarizer having the function of transmitting and blocking outlight is a basic constitutive element in liquid crystal displays (LCD),along with the liquid crystal that functions as a switch for lighttherein. Regarding their application field, LCD were almost forsmall-sized instruments such as electronic calculators and wristwatchesin the early days at the beginning of their development, but in thesedays, they have become much used in other various instruments such asnotebook-sized personal computers, word processors, liquid-crystal colorprojectors, navigation systems for automobiles, and liquid-crystal TV.Given that situation, polarizer for these is required to be improvedmore so as to be free from a problem of irregular coloration thanconventional ones.

[0005] In general, polarizer is fabricated by preparing a polarizingfilm substrate of a stretched and oriented polyvinyl alcohol film (thiswill be hereinafter referred to as “PVA film”, and its raw material,polyvinyl alcohol is a polyvinyl alcohol polymer and this will behereinafter referred to as “PVA”) or of a polyene film (this is preparedby dehydrochlorinating a polyvinyl chloride film or by dehydrating a PVAfilm to thereby make it have a polyene structure therein), followed byapplying thereto a polarizing element of iodine or dichroic dye.

[0006] Of such polarizing films that are obtained by stretching andorienting a PVA film, those having a polarizing element of iodinetherein have good initial polarizing properties, but they are poorlyresistant to heat and water and are therefore problematic in that theirpolarizing properties are worsened when they are used in ahigh-temperature and high-humidity environment. For improving thedurability of such iodine-containing polarizing films, some methods haveheretofore been taken into consideration. For example, PVA for these ismodified or crosslinked, or PVA films are subjected to heat treatment,or the polarizing films themselves are protected with a polymer film oflow moisture permeability. However, any of these methods could not stillproduce satisfactory results.

[0007] On the other hand, polarizing films having a polarizing elementof dichroic dye therein are more resistant to heat and water than thosewith iodine therein, but are problematic in that their initialpolarizing properties are not so good. This is because the molecularweight of dichroic dye is larger than that of iodine and, as a result,PVA films could not well adsorb such dichroic dye and are often unevenlydyed with it. A method was tried of introducing a cationic group intoPVA, a raw material for PVA films, in expectation of improving thedichroic dye adsorbability of the resulting polarizing films (JapanesePatent Laid-Open No. 230606/1985). However, the polarizing films of thetype that contain dichroic dye in the surface or inside the PVA film ofsuch a cationic group-containing modified PVA are still problematic inthat their water resistance is poor.

[0008] For fabricating polarizing films of good water resistance, atechnique was proposed of using a film of an ethylene-vinyl alcoholcopolymer having an ethylene content of from 1 to 24 mol % for thesubstrate of polarizing films (Japanese Patent Laid-Open Nos.100115/1993 and 188624/1996). However, the polarizing films of the typeof which the substrate is of a film of a polyvinyl alcohol polymer withan ethylene group introduced thereinto are also still problematic inthat their polarizing properties are not good when they are dyed withdichroic dye, as so demonstrated in Comparative Example 6 givenhereinunder.

[0009] The present invention is to provide a polyvinyl alcohol film thatis useful for a raw material for polarizing films of which theadvantages are that not only they have good water resistance and goodpolarizing properties but also they are free from the problem ofirregular coloration, and to provide a polarizing film and a polarizerthat comprise the polyvinyl alcohol film.

SUMMARY OF THE INVENTION

[0010] Given that situation, we the present inventors have assiduouslystudied and, as a result, have found that a film of a vinyl alcoholpolymer which contains a specific amount of cationic group-containingunits and contains a specific amount of α-olefin units having at most 4carbon atoms is effective for solving the problems noted above, and havecompleted the present invention.

[0011] Specifically, the invention is a polyvinyl alcohol film of avinyl alcohol polymer that contains from 0.01 to 20 mol % of cationicgroup-containing units and contains from 0.5 to 24 mol % of α-olefinunits having at most 4 carbon atoms.

[0012] The polyvinyl alcohol film of the invention gives a polarizingfilm of which the advantages are that not only it has good waterresistance and good polarizing properties but also it is free from theproblem of irregular coloration, and the polarizing film gives apolarizer also having the advantages as above.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0013] The invention is described in detail hereinunder.

[0014] PVA for use herein for fabricating the PVA film of the inventionis obtained by hydrolyzing a copolymer of a vinyl ester, a cationicgroup-containing monomer and an α-olefin having at most 4 carbon atoms.The vinyl ester includes, for example, vinyl formate, vinyl acetate,vinyl propionate and vinyl pivalate, but is generally vinyl acetate.

[0015] The cationic group-containing units to be introduced into PVA inthe invention are meant to indicate chemical structure units thatdissociate to have a positive charge in an aqueous solution thereof.Specific examples of the cationic group-containing monomer to give suchchemical structure units aretrimethyl-(3-acrylamido-3-dimethylpropyl)ammonium chloride,3-acrylamidopropyltrimethylammonium chloride,3-methacrylamidopropyltrimethylammonium chloride, quaternary ammoniumsalts of N-(3-allyloxy-2-hydroxypropyl)dimethylamine, quaternaryammonium salts of N-(4-allyloxy-3-hydroxybutyl)diethylamine, as well asquaternary ammonium salts of acrylamide, N-methylacrylamide,N-ethylacrylamide, N,N-dimethylacrylamide, diacetonacrylamide,N-methylolacrylamide, methacrylamide, N-methylmethacrylamide,N-ethylmethacrylamide and N-methylolmethacrylamide.

[0016] The content of the cationic group-containing units in PVA fallsbetween 0.01 and 20 mol %, but preferably between 0.05 and 10 mol %,more preferably between 0.1 and 5 mol %. PVA in which the content of thecationic group-containing units is smaller than 0.01 mol % could nothave the effect of the cationic group introduction thereinto. In view ofthe dichroic dye adsorbability of the polarizing film of PVA, thecontent of the cationic group-containing units in PVA is more desirablyat least 0.05 mol %, even more desirably at least 0.1 mol %. On theother hand, PVA in which the content of the cationic group-containingunits is larger than 20 mol % and which contains such chemical structureunits are difficult to produce. In view of the water resistance of thepolarizing film of PVA, the content of the cationic group-containingunits in PVA is more desirably at most 10 mol %, even more desirable atmost 5 mol %.

[0017] α-olefins having at most 4 carbon atoms for use in the inventioninclude, for example, ethylene, propylene, isobutene and 1-butene. Ofthose, preferred is ethylene. The content of the α-olefin units in PVAfalls between 0.5 and 24 mol %, but preferably between 0.8 and 15 mol %,more preferably between 1 and 8 mol %. PVA in which the content of theα-olefin units is smaller than 0.5 mol % could hardly exhibit the effectof modification with such an α-olefin. However, PVA in which the contentof the α-olefin units is larger is more hydrophobic and its solubilityin water is lower, and if so, PVA itself will be poorly soluble in waterand will lose its own characteristics intrinsic thereto. This tendencyis more remarkable in PVA in which the content of α-olefins is largerthan 24 mol %.

[0018] Not detracting from the advantages of the invention, PVA for useherein may be copolymerized with any other copolymerizable ethylenicunsaturated monomer. The ethylenic unsaturated monomer includes, forexample, acrylic acid, methacrylic acid, phthalic acid (anhydride),maleic acid (anhydride), itaconic acid (anhydride), acrylonitrile,methacrylonitrile, acrylamido-2-methylpropanesulfonic acid and itssodium salt, sodium vinylsulfonate, sodium allylsulfonate, ethyl vinylether, butyl vinyl ether, vinyl chloride, vinyl bromide, vinyl fluoride,vinylidene chloride, vinylidene fluoride, and tetrafluoroethylene. Thecontent of the ethylenic unsaturated monomer units in the vinyl alcoholpolymer is preferably less than 10 mol %, more preferably less than 5mol %, even more preferably less than 2 mol %.

[0019] PVA may be modified at its ends with a chain transfer agent whileit is prepared, or may be post-modified. Also if desired, polyvinylacetate to give PVA may also be modified in any desired manner.

[0020] The degree of polymerization of PVA for use in the invention ispreferably at least 20 mPa.s in terms of the viscosity of an aqueous 4wt. % solution of the polymer, in view of the strength, thestretchability, the polarizing properties and the durability of thepolymer film. The viscosity of the aqueous polymer solution definedherein is measured with a Brookfield viscometer while the solution isrotated at 60 rpm with a rotor No. 1 at 20° C.

[0021] Also preferably, the degree of polymerization of PVA does notexceed 1000 mPa.s in terms of the viscosity of the aqueous 4 wt. %solution of the polymer. If the viscosity of the aqueous 4 wt. %solution thereof exceeds 1000 mPa.s, PVA will be difficult to produce.The B-type viscometer rotor to be used in measuring the viscosity ofaqueous PVA solutions of high viscosity may be selected from Nos. 1 to 3in accordance with the high viscosity of the solutions. More preferably,the degree of polymerization of PVA falls between 22 and 500 mPa.s, evenmore preferably between 25 and 250 mPa.s in terms of the viscosity of anaqueous 4 wt. % solution of the polymer.

[0022] The mean degree of hydrolysis of the vinyl ester moiety of PVAfor use in the invention is preferably at least 90 mol %, morepreferably at least 96 mol %, most preferably at least 98 mol % in viewof the durability of the polarizing film to be produced from PVA.

[0023] PVA may be formed into its film, for example, as follows: PVA isdissolved in water, an organic solvent or a mixed solvent of water andan organic solvent to prepare a PVA solution, and this is formed into aPVA film in a casting method, a wet filming method (that comprisesjetting the PVA solution into a bad solvent), a gel filming method (thatcomprises once gelling the PVA solution by cooling it, followed byremoving the solvent from the gel through extraction to give a PVAfilm), or a combination of any of these. Also employable is a meltextrusion method of melting hydrous PVA (this may contain an organicsolvent and the like) and extruding the resulting PVA melt. Of those,preferred are the casting method and the melt extrusion method to givethe intended PVA film, as the PVA film thus produced gives a goodpolarizing film.

[0024] The solvent to be used for dissolving PVA therein in producing aPVA film includes, for example, dimethylsulfoxide, dimethylformamide,dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, andwater. One or more of these may be used herein. Of those, preferred isdimethylsulfoxide, water, or a mixed solvent of glycerin and water.

[0025] The PVA concentration of the PVA solution or hydrous PVA to beused in producing the PVA film preferably falls between 10 and 70% byweight, more preferably between 13 and 55% by weight, most preferablybetween 15 and 50% by weight. If desired, the PVA solution or hydrousPVA may contain any of plasticizer, surfactant and dichroic dye.

[0026] The plasticizer that may be in the PVA solution or hydrous PVA tobe used in producing the PVA film is preferably a polyhydric alcohol.Its examples are ethylene glycol, glycerin, propylene glycol, diethyleneglycol, diglycerin, triethylene glycol, tetraethylene glycol, andtrimethylolpropane. One or more of these polyhydric alcohols may be usedherein either singly or as combined. Of those polyhydric alcohols,preferred is diglycerin, ethylene glycol or glycerin in view of itseffect of improving the stretchability of the PVA film formed.

[0027] The amount of the polyhydric alcohol to be added to the PVAsolution or hydrous PVA preferably falls between 1 and 30 parts byweight, more preferably between 3 and 25 parts by weight, mostpreferably between 5 and 20 parts by weight relative to 100 parts byweight of PVA. If it is smaller than 1 part by weight, the colorabilityand the stretchability of the PVA film formed will be not good; but iflarger than 30 parts by weight, the PVA film formed will be too flexibleand its handlability will be not good.

[0028] The type of the surfactant that may be in the PVA solution orhydrous PVA to give the PVA film is not specifically defined, but ispreferably a nonionic surfactant. Preferred examples of the nonionicsurfactant are alkyl ether-type nonionic surfactants such aspolyoxyethylene oleyl ether; alkylphenyl ether-type ones such aspolyoxyethylene octylphenyl ether; alkyl ester-type ones such aspolyoxyethylene laurate; alkylamine-type ones such as polyoxyethylenelaurylaminoether; alkylamide-type ones such as polyoxyethylenelaurylamide; polypropylene glycol ether-type ones such aspolyoxyethylene-polyoxypropylene ether; alkanolamide-type ones such asoleyldiethanolamide; and allylphenyl ether-type ones such aspolyoxyalkylene allylphenyl ether. One or more of these surfactants maybe used herein either singly or as combined.

[0029] The amount of the surfactant that may be added to the PVAsolution or hydrous PVA preferably falls between 0.01 and 1 part byweight, more preferably between 0.02 and 0.5 parts by weight, mostpreferably between 0.05 and 0.3 parts by weight relative to 100 parts byweight of PVA. If its amount is smaller than 0.01 parts by weight, thesurfactant will be ineffective for improving the stretchability and thecolorability of the PVA film; but if larger than 1 part by weight, thesurfactant will dissolve out of the surface of the PVA film to causesurface blocking of the film, and if so, the handlability of the film isnot good.

[0030] For the dichroic dye that may be in the PVA solution or hydrousPVA to give the PVA film, referred to are those mentioned hereinunderfor coloring the PVA film therewith.

[0031] Preferably, the thickness of the PVA film falls between 5 and 150μm, more preferably between 20 and 100 μm, even more preferably between30 and 90 μm, most preferably between 35 and 80 μm.

[0032] For fabricating polarizing films from the PVA film, for example,the PVA film is colored, monoaxially stretched, set as it is, and dried,and optionally subjected to thermal treatment. In the process, the orderof the steps of coloring, monoaxially stretching and setting the film isnot specifically defined. If desired, the film may be monoaxiallystretched twice or more.

[0033] The PVA film of the invention is suitable to coloration withdichroic dye. In particular, even when the PVA film of the invention iscolored with dichroic dye, its water resistance and polarizingproperties are still good. Another advantage of the PVA film is that itcan be uniformly colored with dichroic dye to give polarizing films freefrom a problem of irregular coloration.

[0034] For coloring PVA films with dichroic dye, one popular methodgenerally employed in the art comprises dipping PVA films in a solutionthat contains dichroic dye. In the present invention, however, dichroicdye may be added to the PVA solution or hydrous PVA to give PVA films,as so mentioned hereinabove, and the condition and the method for thedye addition thereto are not specifically defined.

[0035] In the invention, in case where the PVA film is dipped in asolution that contains dichroic dye, the treatment may be effected inany stage before, during or after the film is monoaxially stretched.Examples of the dichroic dye employable herein are Direct Black 17, 19,154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37,39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168,202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85;Direct Yellow 8, 12, 44, 86, 87; and Direct Orange 26, 39, 106, 107.Even when one dichroic dye is used alone for coloring the PVA films, itsurely gives color polarizing films, but combining two or more dichroicdyes for coloring it is preferred because of its advantages that thepolarizing films thus fabricated in that manner may have the sameabsorption characteristics in the overall wavelength range of visiblelight of from 380 to 780 nm and have a high degree of polarization. Thedichroic dye referred to herein is meant to include organic dyes but notinorganic dyes such as iodine.

[0036] The PVA film of the invention may be colored with not only suchdichroic dye but also with iodine-potassium iodide or the like.

[0037] For monoaxially stretching the PVA film, for example, employableis a wet stretching method of stretching it in a hot bath (this may be adye-containing solution such as that mentioned above, or a setting bathto be mentioned hereinunder), or a dry heat stretching method ofstretching the wet PVA film in air. The stretching temperature is notspecifically defined. In case where the PVA film is stretched in a hotbath (in the wet stretching method), the temperature preferably fallsbetween 30 and 90° C.; but in case where it is stretched in the dry heatstretching method, the temperature preferably falls between 50 and 180°C. The monoaxially-stretching draw ratio (in multi-stage monoaxialstretching, it is the overall draw ratio in all the stretching stages)is preferably at least 400%, more preferably at least 500% in length ofthe nonstretched original film in view of the polarizing properties ofthe polarizing films to be produced from the thus-stretched film. Theuppermost limit of the draw ratio is not specifically defined, but ispreferably at most 800% for uniformly stretching the film. After thusstretched, the thickness of the film preferably falls between 3 and 75μm, more preferably between 5 and 50 μm.

[0038] Optionally, the PVA film thus having received dichroic dye andhaving been monoaxially stretched may be set in any known method, forexample, by dipping it in a water bath that contains boric acid and/or aboron compound. This treatment increases the light transmittance, thedegree of polarization and the durability of the resulting film. Furtheroptionally, the thus-set PVA film may be fixed in a water bath thatcontains a cationic polymer compound.

[0039] The monoaxially-stretched film is dried (for thermal treatment)preferably at a temperature falling between 30 and 150° C., morepreferably between 50 and 150° C.

[0040] The polarizing film thus obtained in the manner as above may befabricated into a polarizer by sticking an optically-transparentprotective film of good mechanical strength to one or both surfacesthereof. The material to form the protective film may be any and everyone generally used in the art for that purpose, including, for example,cellulose acetate films, acrylic films, polyester films, polyolefinfilms, and polyamide films.

EXAMPLES

[0041] The following Examples illustrate the present inventionspecifically, but not limit the scope of the present invention.

[0042] Unless otherwise specifically indicated, % and parts in theExamples are all by weight. The dichroic ratio of the productsfabricated in the Examples is measured according to the method mentionedbelow.

[0043] Dichroic Ratio:

[0044] Dichroic ratio is one index of the polarizing properties ofpolarizing films. This is measured according to the Standard of EIAJ(the Electronic Industry Association of Japan) LD-201-1983. Concretely,using a spectrophotometer with a C light source, each sample is measuredin a visual field of 2 degrees to obtain its transmittance Ts (%) andpolarization degree P (%), and its dichroic ratio is computed accordingto the following equation:

Dichroic Ratio=log (Ts/100−(Ts/100)×P/100)/ log (Ts/100+(Ts/100)×P/100)

Example 1

[0045] To PVA that contains 0.3 mol % of cationic group-containing units(3-methacrylamido propyl trimethylammonium chloride units) and 2.5 mol %of ethylene units and has a degree of hydrolysis at its vinyl acetatemoiety of 99.2 mol % and a Brookfield viscosity (measured as its aqueous4% solution at 20° C. with a rotor No. 1) of 38 mPa.s, added were 12% ofglycerin and water in a hot bath to prepare an aqueous PVA solutionhaving a water content of 85%. The resulting aqueous PVA solution wasjetted through a slit out onto a roll having a surface temperature of70° C., then dried and heated thereon to obtain a PVA film having athickness of 75 μm. To confirm the degree of swellability thereof, thePVA film was swollen in distilled water at 30° C. for 10 minutes withstirring therein. The degree of swellability of the film was 180%.

[0046] The PVA film was monoaxially stretched, colored, set and dried inthat order to be a polarizing film. Concretely, the PVA film was dippedin an aqueous 4% boric acid solution (bath temperature, 55° C.), andthen stretched 6-fold in the monoaxial direction thereof. While keptstretched, this was dipped for 1 minute in an aqueous 0.65% dichroic dye(Direct Sky Blue 6B) solution (bath temperature, 40° C.) to thereby makeit receive the dye, then processed in an aqueous 4% boric acid solution(bath temperature, 35° C.) for 4 minutes, and then dried in hot air at50° C. This gave a polarizing film having a thickness of 30 μm.

[0047] Both surfaces of the thus-obtained polarizing film were laminatedwith a surface-hydrolyzed triacetyl cellulose film, using an aqueoussolution of PVA117H (of Kuraray). This gave a polarizer.

[0048] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.3%, a degree of polarization of 99.7% and adichroic ratio of 39.5. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Example 2

[0049] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains2.0 mol % of cationic group-containing units (3-methacrylamido propyltrimethylammonium chloride units) and 4.5 mol % of ethylene units andhas a degree of hydrolysis at its vinyl acetate moiety of 98.7 mol % anda Brookfield viscosity (measured as its aqueous 4% solution at 20° C.with a rotor No. 1) of 25 mPa.s was formed into a PVA film having athickness of 75 μm. The concentration of the aqueous dichroic dye(Direct Sky Blue 6B) solution was 0.5 %. The thickness of the polarizingfilm obtained was 30 μm.

[0050] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 177%.

[0051] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.0%, a degree of polarization of 99.7% and adichroic ratio of 38.0. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Example 3

[0052] The same PVA film as in Example 2 was monoaxially stretched,colored, set and dried in that order to be a polarizing film.Concretely, the PVA film was stretched 6-fold in dry air at 75° C. inthe monoaxial direction thereof. While kept stretched, this was dippedfor 1 minute in an aqueous 0.5% dichroic dye (Direct Sky Blue 6B)solution (bath temperature, 40° C.) to thereby make it receive the dye,then processed in an aqueous 4% boric acid solution (bath temperature,35° C.) for 4 minutes, and then dried in hot air at 50° C. This gave apolarizing film having a thickness of 30 μm. With that, both surfaces ofthe thus-obtained polarizing film were laminated with asurface-hydrolyzed triacetyl cellulose film, using an aqueous solutionof PVA117H (of Kuraray). This gave a polarizer.

[0053] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 41.9%, a degree of polarization of 99.5% and adichroic ratio of 34.4. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Example 4

[0054] A polarizing film and a polarizer were fabricated in the samemanner as in Example 2 except the following changes: PVA that contains2.0 mol % of cationic group-containing units (3-methacrylamido propyltrimethylammonium chloride units) and 5.2 mol % of ethylene units andhas a degree of hydrolysis at its vinyl acetate moiety of 98.9 mol % anda Brookfield viscosity (measured as its aqueous 4% solution at 20° C.with a rotor No. 1) of 17 mPa.s was formed into a PVA film having athickness of 75 μm. The thickness of the polarizing film obtained was 30μm.

[0055] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 185%.

[0056] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.5%, a degree of polarization of 98.1% and adichroic ratio of 28.0. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Example 5

[0057] A polarizing film and a polarizer were fabricated in the samemanner as in Example 2 except the following changes: PVA that contains2.0 mol % of cationic group-containing units (3-acrylamido propyltrimethylammonium chloride units) and 4.7 mol % of ethylene units andhas a degree of hydrolysis at its vinyl acetate moiety of 98.6 mol % anda Brookfield viscosity (measured as its aqueous 4% solution at 20° C.with a rotor No. 1) of 26 mPa.s was formed into a PVA film having athickness of 75 μm. The thickness of the polarizing film obtained was 30μm.

[0058] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 185%.

[0059] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.1%, a degree of polarization of 99.7% and adichroic ratio of 38.5. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Comparative Example 1

[0060] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA-HC (ofKuraray—this is a non-modified PVA, and has a degree of hydrolysis atits vinyl acetate moiety of 99.9 mol % and a Brookfield viscosity,measured as its aqueous 4% solution at 20° C. with a rotor No. 1, of 25mPa.s) was formed into a PVA film having a thickness of 75 μm. Theconcentration of the aqueous dichroic dye (Direct Sky Blue 6B) solutionwas 1.0%. The thickness of the polarizing film obtained was 30 μm.

[0061] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 190%.

[0062] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.3%, a degree of polarization of 97.4% and adichroic ratio of 25.0. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. Some irregular coloration was seen inthe combined polarizer plates.

Comparative Example 2

[0063] A polarizing film and a polarizer were fabricated in the samemanner as in Example 2 except the following changes: PVA that contains0.2 mol % of cationic group-containing units (3-acrylamido propyltrimethylammonium chloride units) and has a degree of hydrolysis at itsvinyl acetate moiety of 99.6 mol % and a Brookfield viscosity (measuredas its aqueous 4% solution at 20° C. with a rotor No. 1) of 27 mPa.s wasformed into a PVA film having a thickness of 75 μm. The thickness of thepolarizing film obtained was 30 μm.

[0064] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 178%.

[0065] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.0%, a degree of polarization of 98.3% and adichroic ratio of 27.0. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Comparative Example 3

[0066] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains4.7 mol % of ethylene units and has a degree of hydrolysis at its vinylacetate moiety of 99.8 mol % and a Brookfield viscosity (measured as itsaqueous 4% solution at 20° C. with a rotor No. 1) of 30.5 mPa.s wasformed into a PVA film having a thickness of 75 μm. The concentration ofthe aqueous dichroic dye (Direct Sky Blue 6B) solution was 1.0%. Thethickness of the polarizing film obtained was 30 μm.

[0067] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 206%.

[0068] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.5%, a degree of polarization of 97.8% and adichroic ratio of 26.9. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. Some irregular coloration was seen inthe combined polarizer plates.

Comparative Example 4

[0069] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains0.5 mol % of cationic group-containing units (3-methacrylamido propyltrimethylammonium chloride units) and 32 mol % of ethylenic units andhas a degree of hydrolysis at its vinyl acetate moiety of 98.5 mol % wasformed into a PVA film having a thickness of 75 μm. The concentration ofthe aqueous dichroic dye (Direct Sky Blue 6B) solution was 2.0%. Thethickness of the polarizing film obtained was 30 μm.

[0070] Since the PVA used herein did not dissolve in water to give anaqueous 4% solution thereof, its viscosity was impossible to measure.The degree of swellability of the PVA film (measured by swelling the PVAfilm in distilled water at 30° C. for 10 minutes with stirring therein)to be the polarizing film was 115%.

[0071] Both the polarizing film and the polarizer obtained herein weredifficult to color, and their colorability was too bad to evaluate them.

Example 6

[0072] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains1.0 mol % of cationic group-containing units (3-methacrylamido propyltrimethylammonium chloride units) and 2.5 mol % of ethylene units andhas a degree of hydrolysis at its vinyl acetate moiety of 99.0 mol % anda Brookfield viscosity (measured as its aqueous 4% solution at 20° C.with a rotor No. 1) of 27 mPa.s was formed into a PVA film having athickness of 75 μm. The thickness of the polarizing film obtained was 30μm.

[0073] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 180%.

[0074] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 41.9%, a degree of polarization of 99.9% and adichroic ratio of 43.9. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Example 7

[0075] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains1.0 mol % of cationic group-containing units (3-methacrylamido propyltrimethylammonium chloride units) and 4.7 mol % of ethylene units andhas a degree of hydrolysis at its vinyl acetate moiety of 98.8 mol % anda Brookfield viscosity (measured as its aqueous 4% solution at 20° C.with a rotor No. 1) of 26 mPa.s was formed into a PVA film having athickness of 75 μm. The thickness of the polarizing film obtained was 30μm.

[0076] The degree of swellability of the PVA film (measured by swellingthe PVA film in distilled water at 30° C. for 10 minutes with stirringtherein) to be the polarizing film was 177%.

[0077] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.5%, a degree of polarization of 99.2% and adichroic ratio of 34.1. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. No irregular coloration was seen inthe combined polarizer plates.

Comparative Example 5

[0078] PVA that contains 2.0 mol % of cationic group-containing units(3-acrylamido propyl trimethylammonium chloride units) and has a degreeof hydrolysis at its vinyl acetate moiety of 98.7 mol % and a Brookfieldviscosity (measured as its aqueous 4% solution at 20° C. with a rotorNo. 1) of 28 mPa.s was formed into a PVA film having a thickness of 75μm. Measuring the degree of swellability of the film was tried but invain, since the film partly dissolved in water. As having dissolved inthe processing bath used, the PVA film could not be formed into apolarizing film.

Comparative Example 6

[0079] A polarizing film and a polarizer were fabricated in the samemanner as in Example 1 except the following changes: PVA that contains4.7 mol % of ethylene units and has a degree of hydrolysis at its vinylacetate moiety of 98.6 mol % and a Brookfield viscosity (measured as itsaqueous 4% solution at 20° C. with a rotor No. 1) of 29 mPa.s was formedinto a PVA film having a thickness of 75 μm. The concentration of theaqueous dichroic dye (Direct Sky Blue 6B) solution was 1.0%. Thethickness of the polarizing film obtained was 30 μm.

[0080] Measured at its maximum absorption wavelength, the polarizer hada transmittance of 42.1%, a degree of polarization of 98.4% and adichroic ratio of 27.8. Two and the same polarizer plates fabricatedunder the same condition were combined in cross-Nicol, and visuallychecked for irregular coloration. Some irregular coloration was seen inthe combined polarizer plates.

[0081] The polyvinyl alcohol film of the invention gives polarizingfilms and polarizer which are resistant to water and have goodpolarizing properties and which are free from a problem of irregularcoloration, and its usefulness is great.

[0082] Although the invention has been fully described in connectionwith the preferred embodiments thereof, those skilled in the art willreadily conceive of numerous changes and modifications within theframework of obviousness upon the reading of the specification hereinpresented of the invention. Accordingly, such changes and modificationsare, unless they depart from the scope of the present invention asdelivered from the claims annexed thereto, to be construed as includedtherein.

What is claimed is:
 1. A polyvinyl alcohol film of a vinyl alcoholpolymer that contains from 0.01 to 20 mol % of cationic group-containingunits and contains from 0.5 to 24 mol % of α-olefin units having at most4 carbon atoms.
 2. The polyvinyl alcohol film as claimed in claim 1,wherein the α-olefin is ethylene.
 3. The polyvinyl alcohol film asclaimed in claim 1, for which the vinyl alcohol polymer has a viscosityof at least 20 mPa.s as its aqueous 4 wt. % solution at 20° C.
 4. Thepolyvinyl alcohol film as claimed in claim 1, wherein the vinyl estermoiety of the polyvinyl alcohol polymer has a mean degree of hydrolysisof at least 90 mol %.
 5. The polyvinyl alcohol film as claimed in claim1, wherein the film comprises a polyvinyl alcohol polymer obtained byhydrolyzing a copolymer of a vinyl ester, a cationic group-containingmonomer and an α-olefin having at most 4 carbon atoms.
 6. The polyvinylalcohol film as claimed in claim 1, wherein the thickness of the film is5 to 150 μm.
 7. The polyvinyl alcohol film as claimed in claim 1,wherein the polyvinyl alcohol film contains a polyhydric alcoholplasticizer.
 8. The polyvinyl alcohol film as claimed in claim 1,wherein the polyvinyl alcohol film contains a nonionic surfactant. 9.The polyvinyl alcohol film as claimed in claim 8, wherein the surfactantis present in an amount of from 0.01 to 1 parts by weight, based on 100parts by weight of polyvinyl alcohol polymer.
 10. A polarizing filmproduced by stretching the polyvinyl alcohol film of claim
 1. 11. Thepolarizing film as claimed in claim 10, wherein the thickness of thefilm after stretching is 3 to 75 μm.
 12. The polarizing film as claimedin claim 10, for which the polyvinyl alcohol film is colored with adichroic dye.
 13. A polarizer produced by laminating a protective filmon each surface or on one surface of the polarizing film of claim 10.14. A liquid crystal display containing the polarizing film according toclaim 10.